The present application claims priority to Italian Patent Application Serial No. MI 2000A 001005, filed May 8, 2000.
The present invention relates to a novel extensible gripper for clamping the head portions of plastics material plates and thermoforming apparatus for on-line thermoforming plastics material plates including said gripper.
More specifically, the field of the invention is that of the thermoforming apparatus for on-line thermoforming a plate-like plastics material, and which are used for making three-dimensional articles of manufacture in general.
For performing the above processing operations, the plate-like plastics material must be conveyed through a plurality of processing stations, by suitable cooled gripper systems, the gripper of which clamps and holds a plastics material plate at the head portion thereof, or at the sides of the plate which are cross-wise oriented with respect to the plate feeding direction.
In particular, the above mentioned gripping and conveying grippers operate to prevent the hot plate from being deformed before arriving at the molding station, which deformation would generate undesired deflections and/or longitudinal shrinkings.
To fit the length of the gripper to that of the head portion of the plastics material plate to be gripped by the gripper, auxiliary insert elements which are mechanically coupled to the body of the gripper have been conventionally provided.
Moreover, further sliding parts which are laterally driven on a single rail coupled to a supporting central body are provided, said sliding parts projecting from said central supporting body so as to set the desired length of the gripper.
Both the above mentioned prior grippers have the drawback that they cannot be properly cooled or refrigerated, because of their rather complex construction, and that their length can be adjusted exclusively by manual operations. Moreover, in the case of a gripper including sliding parts, the extension of the gripper cannot exceed about 50% of the length of the central supporting body.
In fact, because of the axial single-rail arrangement of the extensible sliding parts, for an extension beyond the indicated value, this prior gripper cannot provide that mechanical support which is necessary for efficiently holding the plastics material plate.
At present, the most simple solution for properly changing the length of the grippers in relationship to that of the head portion of the plastics material plate, is that of fully replacing the gripper with another gripper having the desired size.
This approach provides, with respect to the other mentioned prior grippers, the advantage that the gripper can be cooled through the overall length thereof; however, it has the disadvantage that a number of grippers equal to that of the different-size grippers for gripping the differently sized plastics material plates is required.
To the above it is to be added that, in each case, a manual operation is always necessary for replacing the grippers, which does not allow to automatically adjust their length from the outside of the thermoforming apparatus.
Accordingly, the main object of the present invention is to provide such a gripper for clamping plastics material plates on thermoforming apparatus, the length of which can be easily changed, even in an automatic manner, up to about twice the basic length of the gripper.
Another object of the invention is to provide a gripper of the above mentioned type which, even in a maximum extended condition thereof, is effective to properly mechanically clamp the head portion of the plastics material plate.
Yet another object of the present invention is to provide such a gripper which includes extensible elements and which can be properly cooled through the overall length thereof.
Yet another object of the present invention is to provide an on-line thermoforming apparatus for thermoforming plastics material plates including the mentioned gripper.
The above mentioned objects, as well as yet other objects, which will become more apparent hereinafter, are achieved by a gripper and a thermoforming apparatus for clamping head portions of plastics material plates, in particular for on-line thermoforming apparatus for thermoforming plastics material plates, wherein said gripper comprises means for allowing said gripper to be extended over 50% of a basic or medium length thereof, while providing a mechanical action necessary for efficiently holding said plastics material plate on said thermoforming apparatus.
Further characteristics of the invention are defined in the dependent claims.
With respect to prior grippers for on-line thermoforming apparatus, the inventive gripper provides the advantage that it can be cooled through the overall length thereof, and that it can be properly adjusted, even in an automatic manner, starting from a control device arranged outside of the thermoforming apparatus.
Moreover, the gripper according to the invention provides the advantage that it can be extended even beyond 50% of its basic length, while providing the mechanical force required for efficiently holding or clamping the plastics material plate.